Gravimetric analysis is a technique that can be used to determine the number of moles of water molecules of crystallisation per mole of a hydrated salt, in this case hydrated barium chloride i.e. the value of n in BaCl2.nH2O. The hydrated salt is heated and weighed until there is no further change in mass (heating to constant mass) and the composition can then be determined.
This procedure uses barium chloride. Other possible salts are copper sulphate and magnesium sulphate, among others.
An alternative form of gravimetric analysis involves precipitate formation. A method can be found here.
Composition of hydrated salt – pupil guide
Composition of hydrated salt – Teacher’s guide
Composition of hydrated salt – Risk assessment